Integerizes computation of the least squares for warped motion.
The model is restricted to only Affine. Affine seems easiest
to compute and integerize since it can be split into two 3-dim
least squares problems, as opposed to rotation-zoom which needs
a 4-dim least-squares problem to be solved.
The current implementation requires only one division per block.

BDRATE impact is mminimal. The upgrade to the affine model improves
coding efficiency but integerization also degrades efficiency a
little. Overall there is a net gain of about -0.07% BDRATE on
the lowres set.
BDRATE lowres: -1.113% with ----enable-warped-motion vs. without
(up from -1.044%).

Change-Id: I6b9216ac0737d76f59054293eabee48e17739ec4